Pine:
I: Knotless on three sides
II: In 25-mm thick planks the knot size is limited to 10-12mm, depending on the width.
III: In 25-mm planks, the knots should not be bigger than 15mm in diameter (the size of a 1 euro cent piece).
U/S: Joinery quality
V: Better construction quality for visible work
VI: Normal construction quality

Larch:
I: Knotless on three surfaces
II: In 25-mm thick planks the knot size is limited to 10-12mm, depending on the width.
III: In 25-mm planks, the knots should not be bigger than 15mm in diameter (the size of a 1 euro cent coin).
U/S: Carpentry quality
IV and S/F: Carpentry quality

Southern Yellow Pine:
SAPS (sapwood): Top quality, i.e. defect free wood.
Prime & Better: This is the best quality available in thicker wood (from 2”). The odd knot on the heart side is permissible.